Thats a shame because I think the combat results table (assuming the narrator uses it and just describes the result without actual numbers) is incredibly narrative. The player rolls, the gm decribes what happens in a colourful way and then adjusts the enemies EP accordingly. However if you must tinker, I would keep the use of the d10, so use a d5. However the very important thing to consider is that the table is designed to make the players more heroic, slanting the results so that the enemy inflicts less than the player. if you are going to introduce a new system, make sure that the enemies inflict less damage. Such combats are likely to last longer as there is a chance neither side will inflict any damage each round, so you may have to decrease EP values.

Keep in mind that separating attack and damage rolls is going to mean more time spent rolling dice for both the players and the GM during combat. The existing rules elegantly combine the combat skill contest and damage inflicted into one roll. The end result is the same, with less die rolling and monkeying around with the core rules.

A better solution to separating attack and damage rolls is to simply add modifiers to the combat ratio and damage scores based on the weapons/strength/combat style of the characters and foes they're facing. Many of the Traits in the game rules already do this.

Understandably, some players may wonder why all weapons, from daggers to halberds, inflict the same distribution of damage in the CRT. I do think that some weapons (for example large two-handed swords or heavy battle axes) could receive a +1 or +2 damage bonus plus perhaps a combat skill penalty if wielded by understrength characters. (Although keep in mind that large creatures already deal out extra damage with the Brutal Trait.) Perhaps give daggers a damage penalty of -1 or -2. Characters wielding other weapons, such as spears, might receive a combat bonus vs. opponents armed with shorter weapons.